The present invention relates to thin-film hard magnetic media which permit information to be written to or read from it by the use of a magnetic head, and more particularly to magnetic recording media having either microscopic grooves called texture on its surface or an uneven surface.
Heretofore, magnetic disk drives have been employed so that information can be written to or read from magnetic recording media. For this purpose, the space between a magnetic head and a magnetic recording medium is usually maintained at a very small value, say between 0.2 and 0.3 .mu.m.
If the head makes frictional contact or collides with the recording medium, they will be worn down or get damaged. To avoid this undesirable phenomenon, a floating head slider carrying a magnetic head is used. In particular, because of a speed difference between the slider and the surface of the recording medium a hydrodynamic floating force is produced in the gap between them to maintain the minute space between them.
However, when the magnetic recording medium is stopped, the aforementioned hydrodynamic floating force is not set up and, therefore, the slider is in contact with the medium and locked. Since the surfaces of the slider and of the medium are fabricated quite accurately, the slider may be attracted to the medium when they are at rest or stopped as described above. If the slider is attracted to the medium in this way, a quite large torque is needed to start or stop the medium. Consequently, it may become impossible to start the medium, or the head makes a frictional contact with the medium, damaging the contact surfaces. As a result, they can no longer be used. In this way, various problems take place.
The means normally adopted to solve the above-described problems is to form microscopic grooves called a texture on the surface of the magnetic recording medium or to make the surface of the medium uneven. If the slider is brought into a stop on the medium, the slider is prevented from being attracted to the medium by the texture or the uneven surface.
A known method of forming the texture described above is to etch pits or holes in random directions. A more common method consists in rotating a substrate for a magnetic recording medium and pressing an abrasive tape against the surface of the subtrate by a pair of pressure rolls made from a resilient material such as rubber. Another common method is to press a disklike abrasive rotary member against the surface of the substrate. The obtained texture can be a desired one of various patterns. In one pattern, grooves are coaxial about the center of rotation of the substrate. In another pattern, grooves intersect the circumferential direction of the substrate at an angle that is not constant.
The prior art pattern of the texture on the substrate has been hardly studied. The principle of the prior art method relies only on the formation of grooves or on making the surface uneven. Therefore, even if a desired texture is actually formed on the surface of the substrate, the intended decrease in the friction coefficient between the surface of the recording medium and the magnetic head slider is not one as expected when they are used in practice. Consequently, the contact start and stop (CSS) characteristics and other characteristics of the magnetic recording medium are not satisfactory.
Next we explain the CSS characteristics. A repeated rubbing contact of a magnetic head slider with a magnetic recording medium which occurs at times of ON/OFF of the power switch of a disk driving apparatus causes abrasion and damage of surfaces of the both part.
As the magnetic recording layer on the surface of a magnetic recording medium is especially easy to be damaged, it is necessary to provide lubrication on the surface of the magnetic recording layer. As a contrary phenomenon to the above stated one, sometimes an adhesion of a slider to a surface of a magnetic recording medium occurs. That happens in a case that each of them has an extremely smooth contact surface.
When the adhesion force between the slider and the magnetic recording medium exceeds the torque of the moter which move the magnetic recording medium, it can not be rotated and it does not work. In order to avoid abrasion, damage and adhesion of the recording medium with a magnetic head slider, it is general to make the surface of the recording medium rough (texture formation). That is a general way to improve such characteristics. The characteristics of the surface of the recording medium concerning the adhesion poperties and lubricative properties are called as CSS characteristics.
Some examples are known to arrange the roughness of the textured surface in a determined range. But in such a case it is sometimes difficult to unify the CSS characteristics, for example friction coefficient of the surface of the recording disks. That causes problems concerning reliaility and durability of the magnetic recording disks.
The requirement for higher recording density and more increase of recording capacity of a recording medium is becoming more and more strict. Although it is natural to enhance the accuracy to form the magnetic recording media to reply to the requirement, it is necessary to achieve the most preferable figure of the texture and to improve the CSS characteristics.
Moreover recently in addition to the improvement of the CSS characteristics it is required to improve also the stability of floating properties of the magnetic recording medium and the glide characteristics in relation to the magnetic head.
Next we state the glide characteristics of thin-film hard disk magnetic media. In order to enhance the recording density it is necessary to reduce the size of recording bits on the magnetic recording layer of the media. In order to make the recording bits size smaller it is necessary to reduce the flying height of the magnetic head on the surface of the magnetic recording media. In such cases the floating stability of the magnetic head is important for read/write on the magnetic recording medium. If the slider would collide to uneven portions of the surface of the magnetic recording medium, the stability of the slider would be reduced and it would cause anomalies of reading signals and/or non-uniformity of the bit lengths by a slight change of the recording signals. Moreover the collision of the slider to the uneven portions of a recording medium causes anomalous contacts of the slider with the recording medium.
As stated above it is necessary to keep the surface of the recording medium smooth in order that the slider floats stably on the magnetic recording medium even if the glide height is extremely small. The smoothness of the surface of magnetic recording media is clled as glide charactersistics.
As a result of strict requirement to increase the recording capacity and the recording density, the gap between a surface of a recording disk and a magnetic head slider is required to be more reduced, and such a requirement is difficult to be satisfied by prior arts.